HeaderParam don't work with null headers

[garcia-jj]

public void find(State state, @HeaderParam("ETag") String etag)

If ETag header is null, an exception happens.

20:22:11,223 ERROR [io.undertow.request] (default task-12) UT005023: Exception handling request to /cities/RS.json: java.lang.IllegalArgumentException: Parameter value cannot be null
    at br.com.caelum.iogi.parameters.Parameter.notNull(Parameter.java:24) [iogi-1.0.0.jar:]
    at br.com.caelum.iogi.parameters.Parameter.<init>(Parameter.java:14) [iogi-1.0.0.jar:]
    at br.com.caelum.vraptor.http.iogi.IogiParametersProvider.parseParameters(IogiParametersProvider.java:117) [vraptor-4.0.0.Final.jar:]
    at br.com.caelum.vraptor.http.iogi.IogiParametersProvider.getParametersFor(IogiParametersProvider.java:69) [vraptor-4.0.0.Final.jar:]
    at br.com.caelum.vraptor.http.iogi.IogiParametersProvider$Proxy$_$$_WeldClientProxy.getParametersFor(Unknown Source) [vraptor-4.0.0.Final.jar:]
    at br.com.caelum.vraptor.observer.ParametersInstantiator.getParametersForCurrentMethod(ParametersInstantiator.java:135) [vraptor-4.0.0.Final.jar:]
    at br.com.caelum.vraptor.observer.ParametersInstantiator.instantiate(ParametersInstantiator.java:89) [vraptor-4.0.0.Final.jar:]

[Turini]

doing it